The goal of this project is to determine how specific types of noise-induced cochlear pathologies alter hearing performance and auditory nerve fiber activity. Several types of intense noise will be used to produce different patterns of cochlear lesions in chinchillas. Behavioral conditioning techniques will be used to obtain psychophysical tuning curves, gap detection thresholds and masked audiograms. Auditory nerve fiber activity will be assessed through tuning curves, discharge rate-intensity functions, post-stimulus time and interval histograms, spontaneous discharge rates and two-tone inhibition. The cochlear histopathologies will be evaluated by light and electron microscopy and related to the noise-induced changes in psychophysical measurements and neural activity. The results have implications for understanding how various cochlear structures contribute to normal psychoacoustic phenomena, audiometric disorders and the neural code for hearing.